Single-Shot Multi-light-Direction Searching on Discretized Lighting Space

Abstract

Existing methods for light direction estimation solve the problem only by presupposing certain assumptions, e.g., that only one light illuminates the object, the object has a uniform texture or smoothly varying surface, or there is a known object in the scene. However, these methods cannot be used reliably in real-world settings. We propose a framework that can be used in natural settings to estimate multi-light directions from a single image. To tackle this novel and challenging problem, we divide the lighting space into ranges and formulate the estimation problem as a problem of searching the ranges where the light is cast from a multi-illuminant image. We propose a two-step approach. First, we generate single-illuminant images, one of which assumes that there is only light on one range. Next, we select some images from the candidates that could each be a component of a multi-illuminant image under physical constraints. The experimental results demonstrated that the proposed method outperformed the direct-estimation method when the lighting space is finely divided.